The instant invention relates to methods and apparatus for heating removably attachable rivet headforming dies used by various heading tools which in turn impart curing heat to a plastic rivet during the formation of a head thereon.
The prior art teaches the setting, or more accurately, the softening, head forming and complete polymerization, of a thermoset plastic rivet such as the "Composite Rivet" disclosed in U. S. Pat. No. 4,478,544, issued Oct. 23, 1984, and assigned to the assignee of the instant invention, by applying heat to initially soften, and later to fully polymerize, the "B"-staged head-forming portion of the rivet during the formation of a head thereon by a heading tool comprising a die. However, due to the difficulty involved with the precise application of heat to the head-forming portion of a rivet at the proper instant prior to and during the head forming operation, the prior art has resorted to the use of plastics which remain "B"-staged only at relatively low temperatures. The removal of such a rivet from the low temperature environment at which it is stored to ambient temperature conditions imparts sufficient heat thereto to initially soften, and eventually cause complete polymerization of, the rivet.
It will be appreciated that the controlled delivery of heat to the rivet permits the use of a wider range of matrix materials while facilitating acceleration of the entire "setting" process. In my copending application entitled "Tool for Setting Plastic Rivets," Ser. No. 07/031,654, filed Mar. 30, 1987 now U.S. Pat. No. 4,736,507, and assigned to the assignee of the instant invention, I teach a heading tool featuring removably attachable rivet head-forming dies which may be heated immediately prior to the riveting operation. The heat thus imparted to the removable head-forming dies is thereafter transferred directly to the rivet during head formation thereon, thereby facilitating the softening of the plastic rivet prior to and during head forming, and effecting controlled polymerization of the rivet by virtue of its readily ascertainable heat transfer characteristics. The precise control of die temperature, however, becomes critical to achieving such superior rivet head formation.